As compared to other display devices such as liquid crystal display (LCD) devices, the organic light emitting diode (OLED) display devices are self-emitting apparatuses that do not require a backlight. Having the advantages of fast response, a wider viewing angle, high brightness, more vivid color rendering, thinner and lighter, they have found a wide range of applications in display field. Typically, OLED display apparatuses may be categorized into three types, a top-emission type OLED, a bottom-emission type OLED, and a dual-emission type OLED.